Angry lies about some racehorses (9)
I believe the answer is:
yearlings
'some racehorses' is the definition.
(I know this)
'angry lies about' is the wordplay.
'about' is an anagram indicator.
'angry'+'lies'='angrylies'
'angrylies' with letters rearranged gives 'YEARLINGS'.
(Other definitions for yearlings that I've seen before include "Racehorses in their second year" , "young runners" , "Young horses" .)